Results of this Group's previous work suggest that the metabolic and histologic degeneration of articular cartilage can occur from repetitive impulsive loading. Such loading, even within physiological limits, if not protected against by the natural musculosketal shock absorbing mechanism, has a rapid degenerative effect on articular cartilage and also causes an increase in underlying stiffening of the subchondral bone. The initiation and progression of cartilage damage has been found to be associated with alterations in the local stiffness of this underlying bone. The objectives of the proposed research are: (1) to establish the temporal sequence of bone cartilage changes during the initiation and progression of osteoarthritis and to investigate in particular the role of bony changes in potentiating the progression of cartilage damage. (2) To investigate the natural shock absorbing mechanisms which exist to protect joints from deleterious loading. This work should lead to a better understanding of osteoarthrosis and, hopefully, the techniques for preventing and alleviating joint degeneration.